1. Field of the Invention
This invention relates to a roller holding unit for a pressing tool with a piston-cylinder unit and clamping jaws.
2. Discussion of Related Art
German Patent Reference DE 196 31 019 teaches a pressing device having a pressing pincer for connecting a tube to a press fitting. The pressing pincer includes two pivot arms which are each pivotally articulated by one bolt, respectively, between two equal T-shaped carrier plates. A piston-cylinder unit is actively connected to a roller holder with two rollers. The pivot arms have at one end a roll surface for supporting on the press cylinder of the pressing device. At the opposite end they are designed as clamping jaws with pressing surfaces directed towards one another. The articulations for the bolts are located at a distance on the carrier plates. In the region of the free end of the T-shaped carrier plates, a receiver of a connection bolt is located for the connection with the pressing device. During use of this device, the pressing pincer is pulled to the rear towards the pressing device. In doing so, the pivot arms slide with their roll surfaces along the pressing device to the rear. The tensile force is transmitted via the connection bolt onto the T-shaped carrier plates. Thus, the pivot arms pivot about the bearing bolts, and the pressing jaws are moved towards one another and pressed together.
European Patent Reference EP-1,103,349 discloses a pressing tool which actuates a hydraulic piston-cylinder unit by an electrically operated hydraulic pump. The same is actively connected to a roller holder which includes two rollers. The clamping jaws are connected via a retaining bolt to a fork-like receiver by a T-shaped suspension. The fork-like receiver is part of the piston-cylinder unit. The rollers on the roller holder roll on the clamping jaws of a clamping pincer as soon as the clamping pincer is pulled rearwards by the piston-cylinder unit, and thus the clamping is carried out. In doing so, the clamping pincer is pressed together by the rollers pressing apart the clamping jaws at the rear. With this design, the roller has the shape of a yoke which is rigidly connected to the piston rod. Roller holders, rollers, and roller mountings need to be designed in a solid manner because the full pressing force and the actuation force of the piston-cylinder unit needs to be accommodated by the rollers via their mounting and transmitted to the roller holder. This design requires a corresponding constructional size and dimensioning of the retaining plates and the rollers, roller bearings, and bearing pins. It is accordingly heavy and complicated in its manufacture.
European Patent Reference EP-1 684 948 shows a roller holder unit for an electrically operated pressing tool in which a bearing block for two identical rollers is provided with sliding bearing surfaces, the form of which corresponds to the roll surface and thus to the outer diameter of the roller. This design has the disadvantage that in the area of the sliding bearing surfaces and between the rollers, dirt particles can accumulate which, after a certain time, can result in plugging, and thus seizing.